1. Field of the Invention
This invention generally relates to the field of glass compositions and devices for optical amplification.
2. Description of the Related Art
In optical telecommunications networks, high bandwidth is desired for applications such as the Internet, video on demand, and videophone. In many optical communications systems, optical signals having wavelengths in the range 1530-1560 nanometers (nm) are utilized. This wavelength range corresponds to the xe2x80x9cC-bandxe2x80x9d in telecommunications. This wavelength range also corresponds to a minimum attenuation region for silica and silica-based fibers.
Optical amplifiers are utilized to amplify the optical signals in those wavelength regions. Conventional optical amplifiers for telecommunications include erbium (Er)-doped silicate glass. The Er-doped silicate glass optical amplifier operates in the C-band and can also amplify optical signals in the 1570 nm-1620 nm range (also referred to as the L-band).
In order to increase optical bandwidth, more wavelengths will need to be transmitted. One wavelength range of interest is the 1460 nm-1520 nm wavelength band, often referred to as the xe2x80x9cS-band.xe2x80x9d However, this wavelength band is outside of the Er-based material amplification range.
Within the 1460 nm-1520 nm wavelength band, trivalent thulium (Tm3+) has an emission band centered at about 1470 nm. With respect to the Tm3+ energy levels, the 3H4xe2x88x923F4 transition in Tm3+ corresponds to the emission at about 1470 nm. In order to generate a population in the 3H4 energy level, for example, 790 nm radiation is absorbed by the Tm3+ material, whereby ions are transferred to the 3H4 excited state from the 3H6 ground state.
Tm-doped silicate glass has an excited state lifetime (for the 3H4 level) of about 10 microseconds, due to the quenching of the upper level in silicate hosts. This short lifetime is less preferable for laser and amplification applications. Similarly, other Tm hosts, such as phosphate glass and borate glass, are also less preferable because Tm3+ is quenched by the high phonon energy of these glasses.
A thulium-doped germanate glass suitable for making S-band amplifying optical fiber is described in the commonly owned and copending U.S. Patent Application entitled xe2x80x9cThulium-Doped Germanate Glass Composition and Device for Optical Amplification,xe2x80x9d by Dejneka, et al., which is incorporated herein by reference. While core and cladding compositions may be made from these materials, and suitable fibers drawn, the expense of the germanate starting materials is significant. As such, fibers with both core and cladding made from germanate materials are not economical to produce. As the light amplification occurs in the core of the fiber, and the glass portion of the fiber is over 99% cladding material, it is highly desirable to use a less expensive glass as the cladding. Such a glass must be property-matched to the germanate core.
Thus, there remains a need for a property-matched cladding material for thulium-doped germanate core optical fibers.
In view of the foregoing, according to one embodiment of the present invention, a borosilicate glass composition comprises SiO2 having a concentration of about 40 mole percent to about 60 mole percent; B2O3 having a concentration of about 10 mole percent to about 30 mole percent; and a first compound selected from the group consisting of MgO, CaO, SrO, BaO, BaF2, MgF2, CaF2, SrF2, BaCl2, MgCl2, CaCl2, SrCl2, BaBr2, MgBr2, CaBr2, SrBr2, Li2O, Na2O, K2O, Rb2O, Cs2O, LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, and combinations thereof, and having a concentration of 10 mole percent to about 40 mole percent.
According to another embodiment of the present invention, an optical fiber amplification device comprises a borosilicate glass material cladding. The core comprises a germanate glass material doped with Tm3+. The germanate glass material has a first surface configured to receive an optical signal having a wavelength of from about 1400 nm to about 1540 nm and a second surface configured to output an amplified optical signal. The borosilicate glass material can have the composition described above.
The borosilicate cladding glass described herein results in a number of advantages. Fore example, it is about 50 times less expensive than a germanate based material. It is property-matched to the germanate core, and has an index suitable for the production of fiber with germanate core materials.
Other advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.